How much do you know about sharks?

Sharks underwater
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How savvy are you about these predators of the deep? Test your knowledge with this quiz!

Question 1 of 12

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shark jaws
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When did sharks first appear in the oceans?

Sharks began to roam the seas between 420-455 million years ago. This makes them older than almost any vertebrate on the planet; and indeed, sharks were around before dinosaurs walked the Earth. Those early sharks are the ancestors of today’s shark species. Most of today’s 400+ species of shark can be traced back to around 100 million years ago.

Question 2 of 12

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shark skin
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Shark skin is fascinating. The scales or denticles are tooth-shaped, which helps the shark travel more quickly through the water. Shark skin has inspired which biomimetic invention?

Scientists interested in biomimicry have had their eye on shark skin for some time because the time-perfected scales that keep sharks free of troubling parasites can also be used to solve human problems. From the obvious applications — suits that speed swimmers through the water and coatings for boats that reduce the number of hitchhikers on the hull — shark skin has also been the inspiration for medical device coatings that keep bacteria from adhering to a surface. That's biomimicry at its best!

Question 3 of 12

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shark nose
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Sharks are famous for their sensitivity to the scent of blood. The most sensitive species can detect:

A shark's sensitivity to the smell of blood varies depending on species, current, the speed of the shark and other factors. But some species can sense blood at a miniscule 1 part per 10 billion, which is the equivalent of a single drop of blood in an Olympic-sized swimming pool. Some other sharks aren't as adept; the lemon shark can only (only?) sense prey at one part per 25 million. 

Question 4 of 12

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blue shark
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What is the smallest species of shark in the world?

Wait, what? Yes, all of the above. The leading contender for smallest shark species is the dwarf lanternshark. However, that's not definitely the smallest species. Guinness Book of World Records explains it like this: "Due to the difficulties in determining precisely when a small species is sexually mature, there are two, possibly three, contenders for the smallest species of shark." The dwarf lanternshark has males at 6.3-6.8 inches (but one male measured 7.4), while the spined pgymy shark females come in at 7.4-7.8 and the pygmy ribbontail catshark has males at 7-7.4 inches. So if you guessed wrong on this question, don't feel bad. Seriously.

Question 5 of 12

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seven gill shark
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Sharks drown when they stop swimming, so they have to stay in continuous movement.

Growing up, you may have learned that sharks have to swim continually to keep water moving over their gills — otherwise they wouldn't be able to breathe. This is true in many cases, but not all. Some species like great whites, reef sharks, mako and salmon sharks have to stay on the move. However many species of shark have special muscles called spiracles, which are found in an opening behind the eyes. Spiracles pump water over the gills, which is how carpet sharks can lie in wait on the ocean floor, ambushing prey as it swims past.

Question 6 of 12

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shark leaping from water
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Sharks' biggest natural predator is:

Sharks may be apex predators in the ocean, but humans are the apex predators of the planet. And sadly, sharks aren't immune to our ridiculous appetite. We kill somewhere between 73 million and 80 million sharks per year. (Meanwhile, only 64 people have been reported killed by great white sharks since 1580.) Sharks caught as bycatch by commercial fishing vessels and human hunting of sharks has decimated populations; between 20-30 percent of shark species are near extinction. As a long-lived creature, sharks mature slowly and can't reproduce quickly enough to avoid a population crash. Over-fishing sharks has serious consequences, because an ecosystem without a top predator is thrown horribly out of whack.

Question 7 of 12

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icy water
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Which species of shark lives in the coldest waters?

The Greenland shark loves cold water, and prefers water between 30.9 to 50.0 degrees Fahrenheit. It is found in the North Atlantic around Iceland, Greenland and Canada. Because it lives in such chilly water and is an ectotherm, it doesn't swim very fast. It has a cruising speed of about three-quarters of a mile per hour. But don't think it can't turn on the jets — this shark can hit a top speed of 1.6 miles per hour. A benefit of living the slow life, however, is a long life, and Greenland sharks are thought to have a lifespan of over 200 years. (By the way, there's no such thing as an Antarctic shark. So if you guessed that one ... gotcha!)

Question 8 of 12

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shark cage
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What is an excessive fear of sharks?

Galeophobia comes from the Greek word "galeos," which was a particular type of shark, and "phobia," which of course means fear. Those with galeophobia become overly anxious at the mere mention of sharks — so activities like visiting an aquarium or riding in a boat in waters where there are sharks would be sheer torture.

Question 9 of 12

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mangrove forest
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Which species of deadly shark is often found in fresh water?

Bull sharks are big, curious, aggressive, have an appetite for a wide range of prey and ... can be found in fresh water. Bull sharks can survive in both salt water and fresh water. Shark Savers explains how: "Osmoregulation is the ability of an organism to maintain a constant concentration of water in its body even when its outside environment would normally cause it to lose or gain water... [B]ull sharks can adapt their osmoregulatory processes to survive in a broad range of water salinities, from the salt water of the ocean to the fresh water of a lake." Bull sharks have been spotted in estuaries, bays, lagoons and more than 2,000 miles up the Amazon from the ocean. They've been found as far up the Mississippi River as Illinois, and they even have been found living happily in a lake at an Australian golf course!

Question 10 of 12

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shark teeth
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Because sharks don't have bones, they don't get cancer.

Scientists used to believe that sharks were immune to cancer. Why? Because sharks' skeletal structure is made of cartilage, and cartilage inhibits the development of blood vessels, which cancerous tumors need to grow. However, sharks are not immune to cancer, and the prevalence of cancer may be higher than we think. Also, ingesting shark cartilage as a way to fight cancer? Well, it doesn't work. In fact, the only thing that powdered shark cartilage accomplishes is the pointless death of countless sharks.

Question 11 of 12

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oceanic white tip
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Which is the fastest species of shark?

Sharks are built like torpedoes (or rather, torpedoes are built like sharks) and many species like the oceanic whitetip shown here are extremely fast. But the fastest of them all is the shortfin mako shark, which has been clocked at 31 miles per hour and even 45 miles per hour. It is believed to possibly hit speeds of 60 miles per hour because it eats sailfish and swordfish, both of which can reach those speeds.

Question 12 of 12

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shark meat
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Which species of shark has poisonous meat?

The Greenland shark has meat so toxic that it's considered poisonous. It contains trimethylamine oxide, which the shark needs for several reasons including that it acts as a natural antifreeze, which is necessary for living in frigid waters. However in humans, it causes effects similar to extreme drunkenness and can cause convulsions and death. The trick to getting around this negative is to make Hákarl, a delicacy of Greenland shark meat that has been buried for six to 12 weeks and has gone through several cycles of freezing and thawing. The only way to make Greenland shark meat edible is to let it rot. Go figure.

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Sharks underwater
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